In gay porn, an older man. The same as a "daddy," but with grey hair.
Usually in their 60's and up.
Matt: "Hey, Emjed! Did you have fun with your silver daddy last night?"
Emjed: "Boy, did I! He was so wrinkly and grey. Mmmm. Mmmm. Good."
Among gay men, an older guy with grey hair who still has a youthful appearance and is considered attractive because of those attributes. Can be in his 30's or 40's. More or less the gay equivalent of DILF.
Wow, that is one hot silver daddy! His short grey hair and gorgeous body turn me on!